Authors of section


Rahul Banerjee, Peter Brink, Matej Cimerman, Tim Pohlemann, Matevz Tomazevic

Executive Editor

Peter Trafton

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Posterior ORIF SI fracture

1. Introduction

A crescent fracture is a fracture dislocation of the SI joint.

This injury involves a ligamentous disruption of the inferior part of the SI joint, and a vertical fracture of the posterior ilium that extends from the SI joint and exits the iliac crest.

The posterior superior iliac spine remains firmly attached to the sacrum via the superior portion of the posterior ligamentous complex.
The remaining anterior fragment is more mobile to internal rotation but remains relatively stable to external rotation and vertical forces.

This fracture is always combined with an injury to the anterior pelvis, most often fractures of the pubic rami.

These fractures are unstable.

orif posterior si fracture fixation

When reducing and fixing the fracture of the iliac wing, the SI joint is indirectly reduced and the function of the posterior ligaments is restored.

orif posterior si fracture fixation

Note to preparation and approach

To allow a good reduction of the fracture, the posterior approach to the SI joint should be made slightly medial to the posterior iliac spine. One should not dissect through the gluteal muscles, but rather lift them from their attachment. This is to facilitate reduction and avoid invagination of the soft tissues.

Alternatively if the crescent fragment is large, fixation can be performed via an anterior approach.

orif posterior si fracture fixation

The patient is placed in a prone position. The thorax and abdomen should be placed on chest rolls without any pressure to the pelvis to facilitate manipulation of the pelvis as well as to facilitate ventilation of the patient during the operation.

orif posterior si fracture fixation

Choice of fixation

Depending on the fracture line, the type of fixation may vary.

orif posterior si fracture fixation

With small fragments, an additional SI screw may provide additional stability of the fixation.

orif posterior si fracture fixation

2. Reduction

Preparation of fracture site

The fracture is exposed with a laminar spreader, cleaned of debris, interposed periosteum, and ligaments.

orif posterior si fracture fixation

The fracture is reduced using pelvic clamps and reduction forceps. In some cases additional Schanz screws are inserted and used as joysticks.

orif posterior si fracture fixation

If the hemipelvis is displaced posteriorly, a slight rotation of the patient to the contralateral side may facilitate the reduction.

orif posterior si fracture fixation

Reduction of the SI joint can be verified by palpating the anterior SI joint surface.

orif posterior si fracture fixation

Temporary fixation

K-wires are inserted for temporary fixation.

orif posterior si fracture fixation

3. Fixation

Plate selection

For large fragments, a 3.5 mm reconstruction plate is used. In osteoporotic bone, an angle stable plate is preferred.

orif posterior si fracture fixation

The plate is shaped to fit the contour of the bone and placed on the lateral rim.

Fixation is completed using bicortical screws.

si joint

If the fracture plane is perpendicular to the iliac wing, stability may be increased using cancellous lag screws in addition to the plate.

Screws should not be used alone unless the bone quality is good.

orif posterior si fracture fixation

If the crescent fragment is small, a plate may not provide sufficient hold. Additional stability can be achieved by insertion of a SI screw.

The SI screw is inserted following the same principles as for the fixation of a SI dislocation.

orif posterior si fracture fixation

4. X-rays

After completion of internal fixation, confirm the final reduction and hardware position intraoperatively by AP, inlet and outlet radiographic imaging.

operative treatment
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